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Tragedy of grasslands revisited

New model gives new perspectives on the tragedy of the commons

- Accounting for ecosystem dynamics combined with economic incentives gives new perspectives on the tragedy of the commons. This is one of the conclusions from a new study conducted by Centre researcher Anne-Sophie Crépin together with Therese Lindahl from centre partner Beijer Institute of Ecological Economics. Overgrazing is often used as the archetypal example of an environmental dilemma called the “tragedy of the commons". It describes a situation in which multiple individuals (farmers) acting independently in their own self-interest can ultimately destroy a shared limited resource (a grassland) even when it is clearly not in anyone's long term interest for this to happen.Risk of drawing the wrong conclusionsCrépin and Lindahl have revisited this classic case of the tragedy of the commons and present their findings in a forthcoming issue of the journal Environmental and Resource Economics.- One key message of our study is that one should carefully look at the real world situation when modelling a grassland. Using a model, which is not correctly specified might make you draw conclusions that are not only quantitatively but also qualitatively wrong, say Crepin and Lindahl.Challenges conventional wisdomCrepin and Lindahl examine the relationship between animal stock sizes and degradation of grasslands by modelling it as a differential game where each farmer maximizes profits given the ecosystem dynamics of a grassland.

In doing this they challenge the conventional wisdom that a tragedy of the commons will be the result unless farmers cooperate. They show that a tragedy might be exacerbated due to ecosystem dynamics and also show cases where a non-cooperative regime actually might under-exploit the grassland.Their results show that all the parts of the model are important: the choice of how to model cattle response to grass availability, the choice of parameter values and the choice of initial conditions.

Grasslands increasingly degreadingOvergrazing occurs when grasses are exposed to livestock grazing for extended periods of time, or without sufficient recovery periods. It reduces the flow of ecosystem services from the land and often cause problems as desertification and soil erosion.

Today grasslands cover some 40 % of the earth´s surface and are found in every region of the world, except from Greenland and Antarctica.

Unfortunately, 50 % of the grasslands in the developing world, where people are directly dependent on them as a resource and have few opportunities for other livelihoods, are degraded today.